[PATCH libdrm 05/10] xf86drm: introduce a get_real_pci_path() helper

[Eric Engestrom]

On Monday, 2018-06-25 17:39:14 +0000, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov at collabora.com>
> 
> Introduce a helper which gets the real sysfs path for the given pci
> device.
> 
> In other words, instead opening the /sys/dev/char/*/device symlink, we
> opt for the actual /sys/devices/pci*/*/
> 
> It folds three (nearly identical) snprintf's and paves the way of adding
> extra devices (see next patch) a piece of pie.
> 
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---
>  xf86drm.c | 62 ++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 50 insertions(+), 12 deletions(-)
> 
> diff --git a/xf86drm.c b/xf86drm.c
> index d4810740..8ccd528f 100644
> --- a/xf86drm.c
> +++ b/xf86drm.c
> @@ -2992,16 +2992,37 @@ static int drmParseSubsystemType(int maj, int min)
>  #endif
>  }
>  
> +static char *
> +get_real_pci_path(int maj, int min)
> +{
> +    char path[PATH_MAX + 1];
> +    char *real_path = malloc(PATH_MAX);

Why not allocate this on the stack and pass it in?
It would avoid the error handling you had to add in this patch :)

> +
> +    if (!real_path)
> +        return NULL;
> +
> +    snprintf(path, sizeof(path), "/sys/dev/char/%d:%d/device", maj, min);
> +    if (!realpath(path, real_path)) {
> +        free(real_path);
> +        return NULL;
> +    }
> +
> +    return real_path;
> +}
> +
>  static int drmParsePciBusInfo(int maj, int min, drmPciBusInfoPtr info)
>  {
>  #ifdef __linux__
>      unsigned int domain, bus, dev, func;
> -    char path[PATH_MAX + 1], *value;
> +    char *real_path, *value;
>      int num;
>  
> -    snprintf(path, sizeof(path), "/sys/dev/char/%d:%d/device", maj, min);
> +    real_path = get_real_pci_path(maj, min);
> +    if (!real_path)
> +        return -ENOENT;
>  
> -    value = sysfs_uevent_get(path, "PCI_SLOT_NAME");
> +    value = sysfs_uevent_get(real_path, "PCI_SLOT_NAME");
> +    free(real_path);
>      if (!value)
>          return -ENOENT;
>  
> @@ -3114,24 +3135,32 @@ static int parse_separate_sysfs_files(int maj, int min,
>        "subsystem_vendor",
>        "subsystem_device",
>      };
> -    char path[PATH_MAX + 1];
> +    char path[PATH_MAX + 1], *real_path;
>      unsigned int data[ARRAY_SIZE(attrs)];
>      FILE *fp;
>      int ret;
>  
> +    real_path = get_real_pci_path(maj, min);
> +    if (!real_path)
> +        return -ENOENT;
> +
>      for (unsigned i = ignore_revision ? 1 : 0; i < ARRAY_SIZE(attrs); i++) {
> -        snprintf(path, PATH_MAX, "/sys/dev/char/%d:%d/device/%s", maj, min,
> -                 attrs[i]);
> +        snprintf(path, PATH_MAX, "%s/%s", real_path, attrs[i]);
>          fp = fopen(path, "r");
> -        if (!fp)
> +        if (!fp) {
> +            free(real_path);
>              return -errno;
> +        }
>  
>          ret = fscanf(fp, "%x", &data[i]);
>          fclose(fp);
> -        if (ret != 1)
> +        if (ret != 1) {
> +            free(real_path);
>              return -errno;
> +        }
>  
>      }
> +    free(real_path);
>  
>      device->revision_id = ignore_revision ? 0xff : data[0] & 0xff;
>      device->vendor_id = data[1] & 0xffff;
> @@ -3145,19 +3174,28 @@ static int parse_separate_sysfs_files(int maj, int min,
>  static int parse_config_sysfs_file(int maj, int min,
>                                     drmPciDeviceInfoPtr device)
>  {
> -    char path[PATH_MAX + 1];
> +    char path[PATH_MAX + 1], *real_path;
>      unsigned char config[64];
>      int fd, ret;
>  
> -    snprintf(path, PATH_MAX, "/sys/dev/char/%d:%d/device/config", maj, min);
> +    real_path = get_real_pci_path(maj, min);
> +    if (!real_path)
> +        return -ENOENT;
> +
> +    snprintf(path, PATH_MAX, "%s/config", real_path);
>      fd = open(path, O_RDONLY);
> -    if (fd < 0)
> +    if (fd < 0) {
> +        free(real_path);
>          return -errno;
> +    }
>  
>      ret = read(fd, config, sizeof(config));
>      close(fd);
> -    if (ret < 0)
> +    if (ret < 0) {
> +        free(real_path);
>          return -errno;
> +    }
> +    free(real_path);
>  
>      device->vendor_id = config[0] | (config[1] << 8);
>      device->device_id = config[2] | (config[3] << 8);
> -- 
> 2.18.0
> 
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